type enum_type_identifier = (identifier, ..., identifier);
An enumerated type is a a special case of ordinal types and
defines a range of elements which are referred to by
identifiers. Enumerated types are ordered by occurence in the identifier
list. So, they can be used as index types in an array
definition, and it is possible to define subranges of them. Since they are
ordered, they can be compared to one another. The intrinsic function
Ord applied to name_identifier returns the number of occurence
in the identifier list (beginning with zero),
return the predecessor and successor of name_identifier.
Boolean is a special case of an enumerated type.
Ordinal Types, Array Types, Subrange Types, Ord, Boolean, Char, Pred, Succ.